Today’s article will focus on black holes. I am sure you are wondering why I chose this subject. Actually, last week, the famous scientist Stephen Hawking announced his new theory about black holes. In this article, I will try to remind you what is known about black holes and to explain this new theory.
First of all, black holes are regions of space-time having a super strong gravitational effects that prevent everything to escape from inside. Sounds scary hum? Indeed, even light cannot escape from a black hole, which is impressive. The idea is that a huge mass can deform space-time to create a black hole. This idea comes from the general relativity. What is this theory about? We call â€śrelativistâ€ť a theory that considers an object whose speed is not negligible compared to light speed. If the speed is slow enough, the classic mechanics can be applied. The general relativity describes how light (or energy) can have an effect on objects movements. This is the most known discovery of Albert Einstein.

What differs between general relativity and usual gravitation? In general relativity, gravitation is not a force but curve of space-time. This theory predicts effects that are lacking in Newton theory such as universe expansion or black holes. But what does this law say about black holes? After Schwarzschildâ€™s discovery, which describes the space-time curve by giving the expression of its space-time interval, this law considers an object as a sphere centered on the mass. So the mass becomes right outside the sphere radius. For every sphere mass, there is a distance until the center called Schwarzschildâ€™s radius where some strange phenomena appear. For example, if the mass has a shorter radius, then for an observer a bit far away, objects that are approaching this radius seem to immobilize and their clocks seem to stop. Moreover, nothing arising from these masses can be observed except gravitational effects. Theses masses that deform space-time are called black holes because they keep light and everything else trapped inside. The limit from where nothing can escape is called the black hole horizon.

Black holes are characterized by different parameters: mass, charge and angular momentum. These parameters separate black holes into four different categories. The mass is never null whereas the other parameters can be null. When both charge and angular momentumÂ are zero, then the object is called a Schwarzschild black hole. When the black hole does not have an angular momentum but has a charge, it is called a Reissner-NordstrĂ¶m black hole. These object are really unlikely to form because charge is supposed to be rapidly canceled. If the black hole has an angular momentum but no charge, it is then called a Kerr black hole. It is the most common type of black hole and it is the one that is the most interesting for research because it can absorb matter. The last type of black hole is the Kerr type electrically charged. Again, a black hole with a charge is not supposed to exist for the same reason than before. So this last type of black hole is very unlikely to exist. A black hole can be formed everywhere; the only thing that matters is to have a sufficient mass of matter that can be compressed.

So now we come the new theory of Hawking. The new idea is that the information of objects that may have entered the black hole does not disappear even though you cannot see it anymore. Instead, it should be stored in two dimensions in the black holeâ€™s horizon. Yes, the deadly limit between the â€śsafeâ€ť zone and theâ€¦â€ťtoo badâ€ť zone. The object should then be stored a bit like an hologram. This idea may be the beginning of a new way of thinking that can help scientists to improve their knowledge about black holes.

Here is the end of my article, I hope you liked it. It was maybe a bit complicated but this subject is really very interesting and I have to admit that It makes me dream about how small we are in front of all those objects.